1. Field of the Invention
The present inventions relates to a fan, and in particular, to an axial flow fan with an annular structure.
2. Description of the Related Art
Electronic devices generally produce heat during operation, and thus, a heat-dissipating device or a fan is required to dissipate the excess heat. Since the demand for heat-dissipation has increased, fans must offer optimal performance. A conventional axial flow fan 10a is shown in FIG. 1A, having a frame 1 and an impeller 2. FIG. 1B shows a perspective view of the impeller 2. The impeller 2 has a plurality of blades 21 radially arranged. Each blade 21 is, however, long and thin and thus easily deformed and distorted during operation. The quality and performance of the fan is reduced accordingly.
Conventional axial flow fans disclosed in U.S. Pat. No. 5,927,944 and No. 4,287,137 are shown in FIGS. 2 and 3, respectively. In FIG. 2, an axial fan 10b has an integral rotating venturi 3, attached at the tip 22 of each blade 21. Although blade strength is enhanced by the integral rotating venturi 3, the integral rotating venturi 3 blocks the entire side inlet, reducing the total performance of the fan.
FIG. 3 is a schematic view of another axial flow fan 10c, having a plurality of closed loops 4 and a plurality of parallel straps 41 with clearance between adjacent straps. The closed loops 4 and the straps 41 are disposed on the blades 21, forming a grating. An air inlet 12 is located at a side 11 of the frame 1, air is blocked by the grating straps 41 before exiting from the side 11, producing air turbulence. Furthermore, the difficulty in manufacturing the straps 41 increases the total manufacturing cost of the fan.
Hence, the above method does not satisfy the demands of both structural stability and fan performance.